The present invention relates generally to a system for charging electric storage batteries, and in particular. to a system for automatically charging such storage batteries both safely and efficiently.
In charging electric storage batteries primarily intended for use in connection with heavy duty/traction machinery applications, such as fork-lifts, transportation devices, mining equipment, etc., a variety of important considerations must be balanced. For example, since such machinery will generally be rendered inoperative during battery charging, it is extremely important that charge times be minimized to the extent possible. This is to be balanced with the need to assure that the storage battery under charge is not damaged during charging, representing a significant cost in replacement, as well as certain environmental considerations such as gassing (the discharge of hydrogen and oxygen resulting from encountered electrolysis), which is commonly encountered in connection with the charging of such storage batteries.
Particular attention must be paid to such factors during finishing portions of the battery charging process, when battery charging rates must generally be slowed to prevent overcharging of the battery, and the potential for damage which such overcharging can cause. Accordingly, a properly designed battery charger must be capable of charging a storage battery in a minimum amount of time, while correcting for and minimizing gassing to the extent possible, as well as protecting against damage to the storage battery during the charging process.
A variety of battery charging devices have been developed in an effort to accommodate these various considerations. Typically, such battery charging devices will apply a full or maximum charging rate to the battery during an initial portion of the battery charging cycle, and thereafter apply a finishing charge, at a reduced rate, to completely restore the battery to its fully charged state. A variety of devices have been developed in an effort to regulate the charging cycle, particularly its finishing portions, in an effort to both minimize gassing and assure correct charge termination without unduly extending the period of time required to fully charge the storage battery. Examples of battery charging equipment of this type may be had with reference to U.S. Pats. No. 4,396,880; 4,394,611; 4,382,221; 4,371,826; 4,313,078; 4,091,320; 4,045,717; 3,946,299; and 3,736,490.
In each case, the battery charging equipment described generally conducts the finishing portions of battery charging in accordance with voltages and/or currents sensed at the battery's terminals. Although generally providing adequate results, it was found that such systems were not entirely effective in accommodating voltage/current transients which may occur during charging, but which may not be sensed by the battery charger. It therefore remained to develop a system which further increases battery charging efficiency by correctly monitoring rates of change in such parameters during battery charging.